Hydrological models for watershed planning and water resources management: a Decision System Support for Marta River Basin (Central Italy)

摘要

Fresh water is a finite and vulnerable resource, essential to sustain life and with a great economic value in all its competing uses and interactions with natural ecosystems as they strictly depend on water above all. Population and economies under rising growing lead to an increase in water demand while its availability remains constant in time. So that drought is actually an insidious hazard of nature for countries experiencing medium to high water stress due to its scarcity and to changed climate conditions showing a decreased amount of precipitation and higher temperature values. Drought is a severe problem in the Mediterranean basin: international conventions and Institutions such as the World Bank and the International Water Forum all consider the area in need of special attention due to problems resulting from its vulnerability to drought and its requirements for better water management. Moreover the European Community policy is directly involved in water scarcity issues, encouraging project development and actions to mitigate the effects of drought and to investigate measures to avoid or reduce drought risk in Mediterranean regions.The project MEDDMAN is a transnational approach in the field of drought and water management involving competent national authorities, leading research institutes and regional authorities and financed by European Union according to its Interreg III B MEDOCC policy. The DAF Department, Department of Environment and Forestry, Agrarian Faculty, University of Tuscia in Viterbo, has been involved in this project with a study area on Marta River Basin, located in the northern part of Latium region. The project's target is to develop an integrated system, capable of evaluating the state of surface water and groundwater resources in the MEDOCC regions preserving and improving the economic growth, developing efficient tools for sustainable water resources exploitation. Special attention is given to the environmental impacts of extreme meteorological and hydrological events, which affect the means of development and best interest of the locals. The focus is on the understanding of the ‘water system’ dynamics and functioning, enhancing the capability to predict its behavior in view of changes (including climate change), and underpinning its sustainable management and development. A simulation model at catchment scale, has been implemented for Marta river basin using SWAT (Soil Water Assessment Tool) code, developed in 90’s by Dr. Jeff Arnold for USDA-ARS, United States Department of Agriculture, Agricultural Research Service. Swat is a comprehensive model that requires a diversity of information and produce reliable results with a rich dataset at disposal (morphological, soil, climatic, hydrologic data). It enables water balance estimation and models the loading of water, sediments and nutrients from land areas in a watershed or to the stream network from sources not associated with a land area and referred to as point sources, such as treatment plants.iThe simulation period covers the years 1999-2006. The model was calibrated for the period 1999-2002 and then validated for the period 2003-2006. The implemented model shows a substantial reliability and accuracy in providing the watershed response in terms of discharge flowing and timing pointing out a rapid rebound on it as a consequence of heavy rainfall events. Statistical tests confirmed the truthfulness of its results.A good correspondence between observed and simulated values can be obtained also regarding nutrients movement and processes even if the available data were not so complete and comparable in terms of nitrogen and phosphorous, and their compounds, concentrations.Surely, the nitrate concentrations found in the monitoring campaigns carried out by the Regional Agency for Environmental Protection (ARPA Lazio) are quite well represented by model results.Such a hydrological and nutrient transport simulation model, can be certainly a powerful and reliable tool for water and natural resources planning in order to achieve a rational and prudent management of them taking into account anthropic needs (water demand, agricultural activities, wastewater treatment plants, hydroelectric power production and so on) but also ecosystems preservation (ichthyic life requirements, river Minimum Flow Requirement, biological communities and so on) and economic aspects allowing to evaluate and compare benefits, disadvantages and consequences for each suggested or hypothesized technical solution on watershed.For the particular characteristics and past of Marta basin, the implemented SWAT model can provides an overview of its multifaceted response to climatic and human pressures and also an estimation of the future available water resources quantity and quality.To have a general overview of the whole basin hydrologic behavior, a seawater wedge simulation model has been implemented for the coastal alluvial aquifer of Maremma Laziale applying Sharp_sar code (Santini, 2008) modified version of SHARP (Essaid, 1990).When the width of the transition zone is small relative to the thickness of the aquifer, saltwater and freshwater can be assumed as immiscible fluids separated by a sharp interface and this approach reproduces the general position, shape and behavior of the interface. SHARP model couples the freshwater and saltwater domains through the interfacial boundary condition of continuity for flux and pressure.With a simulation period of 10 years, Sharp_sar model was implemented on Maremma Laziale coastal aquifer and the results show that after of a pumping period of 10 years, saltwater intrusion might occur in the area between Fiora river and Arrone stream.The initial condition was set using the Badon-Ghyben (1889) e Herzberg (1901) laws to place the initial interface between fresh and salt water so that to ensure the model results after 10 years of simulation.iiThe interface appears located along the coastline without showing clear signs of intrusive phenomena taking place in the middle and southern part of the coastal aquifer, while a retreat of the fresh water is clear in the northern part of it up to 1.2 km inland, in the area between Fiora river and Arrone stream and then confirming what emerged from the study for the establishment of coastal environmental state “(Chiocchini et al., 2005).Even with several uncertainties on number of existing wells, since it’s not mandatory to declare a private well, on pumping amounts and periods the model results point out a supposed critical area with a particular vulnerability to saltwater intrusion phenomena.Other smallest areas in southern part of the coastal aquifer seem to be interested by saltwater intrusion phenomena falling in Tarquinia municipality.Coupling a SWAT model for hydrologic and nutrients transport simulation and investigation with a saltwater interface simulation model, such as SHARP_sar, for the coastal area of this basin, give the opportunity to take into account the several and different aspects and issues connected with the whole watershed behavior and evolution. A correct planning and management of the available natural resources involve a conscientious water bodies exploitation, with respect to habitats and local animal and plants requirements, avoiding saltwater intrusion phenomena and environmental damage, accomplishing people needs, economic, agricultural and tourist development and income, but, above all, ensuring citizens and buildings safety. In the local and actual context, regarding past and present events in the study area, an incisive and suddenly action from government is hoped in order to restore equilibrium conditions and environmental health for watershed. Going on in making information and investigation results available to all the stakeholders and people involved, directly or indirectly, in Marta river basin management, could allow an increase in awareness and consciousness and lead to quickening planning actions and works in a shared and advantageous way for all. Especially with regards to Minimum Flow Requirement, in relation with the water amount deviated for hydroelectric power generation, a rational regulation of the sluice-gates located on Marta river at the exit of lake Bolsena, is needed to ensure ichthyic life and ecosystem preservation together with simple turbines volumes required to correctly working.A multifaceted and integrated approach could certainly be applied in such a complex problem- solving, with the help of hydrologic and nutrients transport simulation models, saltwater intrusion position and movement simulation models and building all the data and results in a GIS platform as to provide a real and concrete Decision System Support.